This invention relates generally to electric motors and more specifically to a motor with an external rotor and a method for assembling the motor.
An motor with an external rotor or an "inside out motor", of the type to which the present invention generally relates has permanent magnets mounted on an inner surface of a cup-shaped rotor bell. The stator is located inside the permanent magnets on the rotor bell. The stator is shaped to receive a bearing for rotatably mounting a rotor shaft through the stator so that the shaft and rotor bell may rotate relative to the stator as a result of the magnetic interaction of the permanent magnets and the magnetic fields created by energizing windings of the stator. Presently, these motors are electronically commutated and have a sensor for detecting the position of the magnetic poles of the rotor to control the commutation of the motor.
Typically, only one or two windings are wound on a bobbin of an inside out motor. Metal is provided around the bobbin, between the permanent magnets and the windings, to conduct the magnetic flux generated by the energized windings. Opposite ends of a plate are bent down so that the bent down ends may extend across the windings on diametrically opposite sides of the bobbin. The plate also has a central opening and a ring extending from the opening which is received into a central opening of the bobbin. Two substantially identical plates are mounted on axially opposite ends of the bobbin, and are angularly offset so that their bent down ends extend over different parts of the windings.